I feel your pain man. Done stuff like that myself before also. Guess you will have to tear apart the form. I once put a rebuilt transmission back into a car only to look over and see the crankshaft flywheel still setting on the workbench. So I had to tear it all back out again. lol uhggg.

Circular saw as close to the brick work as you can. Slide some more of the form out and cut again. Use some masonite or flexible plywood screws and liquid nails to reassemble your form from the inside.